1. Field of the Invention
The present invention relates to a label printing apparatus. More specifically, this invention relates to an assembly, in such an apparatus, for setting individual printing discs in a printing drum and for shifting the entire printing drum and further to an arrangement for moving a ribbon-type printing medium in operative relation to the printing drum.
Label printing apparatus are widely used to mark products with information useful to the consumer, such as price, as well as information useful to the seller, such as inventory control codes. Recently, it has been proposed that such information be handled by central data processing systems, known as a point-of-sale systems, in order to increase the seller's business operating efficiency and to increase the quality of service given the consumer.
Most fully integrated point-of-sale systems depend on the use of the Universal Product Code (UPC) which is comprised of ten basic characters, corresponding to the numbers 0 through 9, each having two elongated bars of preselected width and spacing. Code characters are arranged in a predetermined order on a label placed on the product which identifies the product and its manufacturer (or distributor or supplier). The point-of-sale systems scan the label, automatically tabulate the consumer's bill and process the inventory control information.
UPC labels may also include standard numeric characters printed above or below the bar code which provide the noted information. Another type of machine readable bar code is known as CODABAR (a trademark of Pitney-Bowes, Inc., the assignee of the present invention) and it may include alpha or numeric characters printed above or below its bar code. Accordingly, label printers that complement point-of-sale systems using the above codes have been devised to print both forms of the same information.
2. Description of the Prior Art
A hand-held apparatus suitable for printing UPC labels in the form described above is disclosed in U.S. Pat. No. 3,926,110 (Hubbard et al.), assigned to the assignee of the present invention. This apparatus includes a frame and a drum housing mounted for pivoted movement in the frame. A printing drum, mounted in the housing, comprises a plurality of printing discs each of which has a series of ten die groupings about its periphery. Each grouping has a bar code character printing die and a peripherally displaced, corresponding alpha-numeric character printing die. Every disc may be set to longitudinally align an array of die groupings on adjacent discs across the drum in a printing position. A printing medium, such as a non-woven ink-carrying ribbon, is drawn with a label under the bar code character dies in the aligned groupings by a rotating sprocketed platen to transfer ink to the label in a first bar code area. After the bar code has been printed, the entire drum is rotated or shifted slightly to place the alpha-numeric character printing dies in contact with the printing medium and the label. Thus, ink is transferred to the label in a second alpha-numeric area.
While the Hubbard et al. device operates smoothly and efficiently to print UPC labels, it has certain practical drawbacks. Since the bar code characters are scanned by a laser scanner, they must be precisely and uniformly printed. Accordingly, the printing discs are manufactured to small tolerances and are fit tightly together in the printing drum. Relatively high friction forces are developed between the discs. Therefore, it is difficult to set each disc to print the characters comprising the desired die grouping without disturbing adjacent discs.
Moreover, the ink-carrying ribbon in the Hubbard et al. device is conducted from one exposed spool to another. The ribbon is threaded through the device by hand in an operation which can be messy and time consuming.
Other printing devices have been proposed which include multidisc printing drums incorporating a locking arrangement for simplifying the disc setting operation. For example, U.S. Pat. No. 1,341,021 (Robbins) discloses a printing head for marking machines which comprises a spur gear engageable with any one of the printing discs, and a locking member which fits in an external groove in each disc with the exception of the one engaged by the spur gear. The locking member and spur gear may be shifted simultaneously so that all discs may individually be set.
U.S. Pat. Nos. 1,188,828 (Putnam et al.) and 1,713,528 (Glass) disclose devices similar to that described in the Robbins Patent. However, none of these three devices is designed to print on a label drawn past a printing die or to rotate or shift the entire printing head or drum to print two different character types in the same print cycle. Accordingly, none provides means for simultaneously locking of all discs. Further, force exerted by the locking member in each device is the same at all times during the disc setting and printing operations.